class_docstr: A MultiObjectiveFunction class used to hold multi-objective functions.
code: def functions(self, functions: List[callable]) -> None:
      if not isinstance(functions, list):
          raise e.TypeError("`functions` should be a list")
  
      self._functions = functions
  
file_path: opytimizer/opytimizer/functions/multi_objective/standard.py
imports: from typing import List
  import numpy
  import opytimizer.utils.exception
  from opytimizer.core import Function
  from opytimizer.utils import logging
label_desc: Use image node_id 4 for calling the MultiObjectiveFunction obj's underlying member method code with example usage: obj.functions(functions) without return types